It may be generally stated that when a patch having a drug effect is attached to skin or the like, the drug serving as the active ingredient of the patch is released, passes through the skin and permeates to the blood, thereby exhibiting satisfactory bioefficacy in the body. In order to maintain a stable concentration of the drug in the blood to increase its bioavailability, the releasability of the drug from the patch must be favorably maintained. For this purpose, it is important to avoid impairment of the drug release property of the patch during the period lasting from preparation of the patch to the moment of its use.
The drug will usually be included in the adhesive of the patch, and thus if the patch is allowed to stand in air the solubility of the drug in the adhesive substance is reduced, tending to cause separation of the drug by crystallization. This results in the problem of a lower drug release rate from the adhesive layer.
Techniques for preventing a lower drug release rate include those disclosed in Japanese Unexamined Patent Publication HEI No. 8-40910, Japanese Unexamined Patent Publication HEI No. 8-325141 and elsewhere, based on such concepts as patch manufacturing environment humidity control, nitrogen substitution and packaging of desiccants with patches. Also, Japanese Unexamined Patent Publication HEI No. 5-39379 discloses a humidity-controlling shaped article containing magnesium sulfate.